In the US, sepsis affects more than 750,000 people annually, with a mortality rate as high as 30%. There is still no effective therapy for patients wih sepsis and septic shock. Excessive neutrophil infiltration is a major determinant of organ injury in sepsis, suggesting that targeting neutrophil trafficking is a rational strategy to reduce sepsis morbidity and mortality. The interaction between neutrophils and activated endothelial cells (ECs) is a key regulator of neutrophil infiltration. We have discovered that milk fat globule-epidermal growth factor-factor 8 (MFG-E8) is able to reduce the number of neutrophils in organs of septic animals. Administration of recombinant human MFG-E8 after sepsis not only attenuated organ damage, but also doubled the survival of septic animals. We have also discovered that cold-inducible RNA-binding protein (CIRP) is released into the circulation in sepsis and functions as a damage-associated molecular pattern (DAMP). We have demonstrated that blocking CIRP activities with CIRP-neutralizing antibodies after sepsis not only inhibited inflammation, but also markedly improved the survival of septic animals. Recently, we have demonstrated that injection of recombinant murine CIRP into healthy mice caused EC activation and vascular leakage in the lungs. One focus of this proposal is to further elucidate the mechanisms responsible for MFG-E8's regulation of neutrophil trafficking and CIRP's control of EC activation. These findings will guide the design and development of new therapeutics for treating sepsis. Due to the complexity and difficulty in developing protein-based biotherapeutics, we focused on identifying small molecule-like oligopeptides derived from MFG-E8 and CIRP. To date, we have identified two candidate peptides, MSP68 and C23, derived from MFG-E8 and CIRP, respectively. We will further evaluate their efficacy, half-life and toxicity for treating sepsis. In this research program, we will address the following three key questions: 1) How does MFG-E8 inhibit neutrophil activation and infiltration in sepsis? 2) How does CIRP cause vascular EC activation and injury in sepsis? 3) Can we develop an anti-sepsis strategy targeting the neutrophil-EC interaction? The proposed research will lead to a new direction for the development of innovative therapeutics to treat patients suffering from sepsis and septic shock.